The present invention generally relates to a sealing system for high temperature and high pressure environments and, more specifically, to a sealing system having a mismatched metal-to-metal seal and an o-ring seal with a vent hole therebetween.
Generally, o-ring type seals are employed in piston or rod sealing applications to provide a seal between two adjacent cylindrical surfaces. These seals are subjected to various external forces and conditions throughout such use. At low pressure and low temperature conditions, seals can accommodate non-uniform pressure distribution due to the nature of their composition, for example, resilient, flexible and elastic materials such as rubber and elastomeric substances. Seals subjected to high pressure, for example, greater than about 3,000 pounds per square inch gauge (psig), and high temperature, for example, greater than about 300 degrees Fahrenheit (° F.) tend to deform, and gradually extrude into, for example, a gap between the adjacent cylindrical surfaces. In addition, elevated temperatures eventually greatly reduce the physical qualities of resilient, flexible, and elastic materials, and cause such materials to buckle under non-uniform pressure distribution. Seals eventually succumb to such high pressure and high temperature conditions, and their replacement becomes necessary.
Engineers have attempted to design more resilient seals by redesigning their shape, for example, increasing/decreasing their diameters, thicknesses, etc., or by altering the seal's composition in order improve their ability to withstand higher temperatures and pressures, and to increase the seal's service life. However, an important design challenge is the machinery parameters themselves, that is, the existing width, depth and diameter of the recessed portion, groove, or gland of the machine's seal surfaces.
A conventional seal design is an o-ring sandwiched between two retainer rings, as described in U.S. Pat. No. 2,456,356. However, this prior art seal design is not tailored to meet the current operating conditions due to its shortcomings described therein. As disclosed in the '356 patent, the o-ring was meant to possess a diameter of greater cross-section than the recessed section, or groove, so that when pressure was applied to the o-ring, the o-ring would force the retainer rings to extrude outside the recessed portion in order to create a static seal. Such a design cannot effectively be utilized in present high pressure and/or high temperature applications. Modern seal designs avoid deforming the ring members to the point of extrusion, in order to prolong the service life of the seal. In present day high pressure and/or high temperature applications, the constant extrusion as described and taught in the '356 patent will cause the seal to deform, buckle and extrude, and fail much sooner than desired.
Another seal design of the prior art incorporates a single composite ring, as described and taught in U.S. Pat. No. 5,269,537. As disclosed in the '537 patent, the composite ring includes an elastomeric seal ring having a circumferentially disposed u-cup end that forms an annular pressure cavity, a highly resilient energizer ring embedded within the seal ring, and an integral anti-extrusion ring located opposite the u-cup edge and bonded integrally to the seal ring. As described, the annular pressure cavity is in fluid communication with an annular passage in order to communicate fluid pressure from the strut to the recessed section, groove or gland, that is, the cavity is exposed to pressurized hydraulic fluid. Although the teachings pertain to high hydraulic pressure applications, the seal's design becomes less than desirable and even potentially hazardous when applied to a pneumatic application involving gas turbine engines. Such high pressure/high temperature applications would continually expose not only the annular pressure cavity, but also the u-cup and its two “legs,” to extreme operating conditions without protection. The seal design of the '537 patent did not contemplate the deleterious effects of high pressure and/or high temperature conditions of pneumatic applications, and consequently could not effectively endure such operating environments.
Metal-to-metal seals have been conventionally used for connecting together two metal tubes. U.S. Pat. No. 6,045,165 describes a tube connector/coupling created by the deformation of the male tube member to form two metal-to-metal sealing surfaces with the female member. The deformation of the male tube under rotational torque forms an annular metal-to-metal seal between the male tube outside diameter and the female connector inside diameter. A second metal-to-metal sealing surface is formed as the tip of the tube butts against an internal shoulder of the female connector. The sealing system of the '165 patent, however, due to its requirement for metal deformation under rotational torque, may not be useful in circumstances where such deformation is undesirable, such as in cases were removal of one part and replacement thereof may be needed.
Referring to FIG. 1, a high pressure, high temperature compressor assembly 10 may generally comprise a housing 11 having a chamber 12 containing a first port 14 and a second port 16. Chamber 12 may support a piston 18 positioned for selective movement within chamber 12. To ensure that a static seal exists between chamber 12 and first port 14, a sealing unit 20 may be employed and supported in a recessed portion 22 of chamber 12. Sealing unit 20 may be positioned in recessed portion 22 in order to maintain a static seal under temperatures in excess of about 380° F., and typically about 400° F., and more typically about 500° F.; and pressures of at least about 1,750 psig and greater than about 5,000 psig, and typically greater than about 6,000 psig, and more typically greater than about 7,000 psig. To cool assembly 10 during operation, a polyalphaolefin coolant (“PAO feed”) may be fed through a cooling channel 28 disposed within and supported by chamber 12, and disposed between chamber 12 and housing 11, and proximate to sealing unit 20. The PAO feed may circulate at about 200 psig and about 180° F., for example, in order to prevent assembly 10 from overheating. Under typical operating conditions, the external temperature gradient acting upon housing 11 proximate to sealing unit 20 may typically be in excess of about 400° F., and more typically about 500° F. due to external pressures exceeding about 5,000 psig, and typically about 6,000 psig, and more typically 7,000 psig that act upon assembly 10.
The sealing system of FIG. 1 may however, after several cycles, begin to leak. Air recharge systems (ARS) require long lasting (>5,000 cycles) seals for the high pressure (>5,000 psig), high temperature (>400° F.) environment of the ARS compressor. A small amount of leakage from either seals 20, 28 may cause serious failure in the compressor.
As can be seen, there is a need for a sealing system able to operate under conditions such as pressures greater than about 5,000 psig and temperatures greater than about 400° F. without experiencing deformation, buckling, and extrusion. There also exists a need for a seal capable of maintaining a longer service life than seals that are presently commercially available.